The present invention relates to a cemented carbide tool for cutting, punching or nibbling which, by means of a special way of manufacturing, has surprisingly better properties in comparison to those of conventional tools.
The manufacture of sheet metal parts is normally done by cutting and punching. By both of these methods the parting of the material occurs between two edges working against each other. The yield point of the material is exceeded at sufficiently a high cutting or punching force.
Nibbling is used for the purpose of cutting contours in normally 3-10 mm thick sheet metal. Cylindrical punches of steel or cemented carbide are most frequently used in a nibbling machine. They perforate the sheet metal by a movement perpendicular to the metal through a die used as a dolly. When nibbling and punching holes, different widths of the slot in the die are used, which are adjusted to suit the composition and sheet thickness of the material. When a so-called "wide slot" is being used, the cutting, when nibbling is taking place, depends on both shear and tensile forces. Using a narrow slot, the cutting of the sheet takes place due to pure shear forces.
The normal wear pattern of a steel nibbling punch is that material by abrasion is worn off and moved up along the punch. Because of the wear pattern, the punch turns conical which in turn finally causes an increased friction force that changes the cutting quality to an unacceptable level. When using cemented carbide punches, this wear process is considerably slower, but with the same result as obtained by the used of steel punches. Due to the brittleness of the cemented carbide the risk of fracture is great. As a result, cemented carbide punches are used only exceptionally. In U.S. Pat. No. 4,743,5I5, there is disclosed a cemented carbide preferably for use in rock drilling but also for wear parts and other parts exposed to wear. It is characterized by a core containing eta-phase surrounded by cemented carbide free from eta-phase.